The recent miniaturization and integration of semiconductor integrated circuits have led to a demand for increasing resolutions of semiconductor exposure apparatuses (hereinafter referred to as “exposure apparatuses”). Accordingly, advances are being made to reduce wavelengths of light emitted from exposure light sources. Typically used as exposure light sources are gas laser apparatuses instead of conventional mercury lamps. A gas laser apparatus used as an exposure light source may include, for example, a KrF excimer laser apparatus that outputs an ultraviolet laser beam at a wavelength of 248 nm and an ArF excimer laser apparatus that outputs an ultraviolet laser beam at a wavelength of 193 nm.
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